The present invention relates to a semiconductor device for constituting an active matrix drive portion in a reflection type liquid crystal display apparatus for active matrix display, a reflection type liquid crystal display apparatus for active matrix display, and a reflection type liquid crystal projector using a reflection type liquid crystal display apparatus for active matrix display.
As a reflection type liquid crystal display apparatus for active matrix display, the one shown in FIG. 7 has been considered.
The reflection type liquid crystal display apparatus 9 is comprised, as a whole, of a liquid crystal layer 33 formed by injecting a liquid crystal between a semiconductor device portion 50 constituting an active matrix drive portion and a counter transparent substrate 32 provided with a counter transparent electrode 31 functioning in common for each pixel.
The semiconductor device portion 50 comprises a semiconductor substrate (base semiconductor region) 11 such as a silicon substrate of a first conduction type, for example, P type, on which switching transistors 13 and signal accumulation capacitors 55 are provided on the basis of each unit region for constituting a pixel Px.
The switching transistor 13 is configured as a MIS (Metal Insulator Semiconductor) type or MOS (Metal Oxide Semiconductor) type transistor in which a source region 13S and a drain region 13D of a second conduction type (namely, of N type where the semiconductor substrate 11 is of P type) are formed on the semiconductor substrate 11, and a gate electrode 13G formed of polysilicon or the like is formed on the region between the source region 13S and the drain region 13D, with a thin insulating layer 12a therebetween which constitutes a part of an insulating layer 12 formed of silicon dioxide or the like.
The signal accumulation capacitor 55 is configured as a MIS type or MOS type transistor in which semiconductor regions 55D and 55S of the same second conduction type as that of the source region 13S and the drain region 13D of the switching transistor 13 (namely, of N type where the semiconductor substrate 11 is of P type) are formed on the semiconductor substrate 11, and an electrode 55G is formed on the region between the semiconductor regions 55D and 55S, with a thin insulating layer 12b therebetween which constitutes a part of the insulating layer 12. With an appropriate potential impressed on the semiconductor regions 55D and 55S, a channel 55c is formed at a portion beneath the electrode 55G between the semiconductor regions 55D and 55S, and a capacitance is formed.
Furthermore, high-concentration bias semiconductor regions 57 of the same first conduction type as that of the semiconductor substrate 11 (namely, of P type where the semiconductor substrate 11 is of P type), for impressing a bias potential such as earth potential on the semiconductor substrate 11, are formed on the semiconductor substrate 11 on the basis of each unit region constituting a pixel Px.
In addition, on an insulating layer 14 formed on the insulating layer 12, a scan line (scan electrode) 21 is formed in connection with the gate electrode 13G of the switching transistor 13, a signal line (signal electrode) 23 is formed in connection with the source region 13S of the switching transistor 13, a wiring 25 is formed for interconnection between the drain region 13D of the switching transistor 13 and the electrode 55G of the signal accumulation capacitor 55, and a bias electrode 59 is formed in connection with the semiconductor regions 55D and 55S of the signal accumulation capacitor 55 and with the bias semiconductor region 57.
Furthermore, on an insulating layer 16 formed on the insulating layer 14, a reflection electrode 19 for constituting a pixel electrode is formed in connection with the wiring 25, i.e., in connection with the drain region 13D of the switching transistor 13 and the electrode 55G of the signal accumulation capacitor 55.
The reflection type liquid crystal display apparatus 9 has a structure in which a multiplicity of the scan lines 21 are arranged in a vertical direction of a display screen, a multiplicity of the signal lines 23 are arranged in a horizontal direction of the display screen, and each of the portions at intersections of the scan lines 21 and the signal lines 23 is constituted as the pixel Px as above-mentioned.
With the bias electrode 59 earthed, an earth potential impressed on the semiconductor regions 55D and 55S of the signal accumulation capacitor 55 and the bias semiconductor region 57, and with a predetermined potential impressed on the counter transparent electrode 31 functioning in common for each pixel, the scan lines 21 are sequentially selected by a scan line drive circuit, and a predetermined potential is impressed on the gate electrode 13G of the switching transistor 13 for the pixel connected to the scan line 21 thus selected, whereby the switching transistor 13 for the pixel under consideration is turned ON, and a signal voltage is impressed on the source region 13S of the switching transistor 13 for the pixel in consideration through the signal line 23 by a signal line drive circuit, whereby a signal charge is accumulated in the capacitance of the signal accumulation capacitor 55 for the pixel under consideration through the drain region 13D of the switching transistor 13 for the pixel under consideration.
The signal charge thus accumulated is impressed on the reflection electrode 19 for the pixel under consideration, an electric field according to the signal voltage is impressed between the counter transparent electrode 31 functioning in common for each pixel and the reflection electrode 19 for the pixel under consideration, and, according to this, the rotatory polarization of light at the portion of the pixel under consideration is controlled by the liquid crystal layer 33. Then, the light which is incident on the reflection type liquid crystal display apparatus 9 from the outside of the counter transparent substrate 32, is transmitted through the portion of the pixel under consideration of the liquid crystal layer 33, is reflected by the reflection electrode 19, is again transmitted through the portion of the pixel under consideration of the liquid crystal layer 33 and goes out to the outside of the counter transparent substrate 32 is modulated, and the light in a predetermined polarization direction is transmitted, whereby an image is displayed on the reflection type liquid crystal display apparatus 9.
However, in the semiconductor device portion 50 in the reflection type liquid crystal display apparatus 9 according to the related art shown in FIG. 7 and described above, the semiconductor regions 55D and 55S constituting the signal accumulation capacitor 55 are of a conduction type different from that of the semiconductor substrate (base semiconductor region) 11, i.e., they are of the same conduction type as that of the source region 13S and the drain region 13D of the switching transistor 13. Therefore, for separation between the switching transistor region and the signal accumulation capacitor region, the distance between the switching transistor region and the signal accumulation capacitor region, i.e., the distance d between the drain region 13D of the switching transistor 13 and the semiconductor region 55D of the signal accumulation capacitor 55 must be large at least to a certain extent. As a result, the area of the pixel Px is large, and the number of pixels which can be formed in a predetermined size is small.
In addition, since the semiconductor regions 55D and 55S constituting the signal accumulation capacitor 55 are of a conduction type different from that of the semiconductor substrate (base semiconductor region) 11, the bias semiconductor region 57 of the same conduction type as that of the semiconductor substrate 11, for impressing a bias potential such as an earth potential on the semiconductor substrate 11, must be formed on the semiconductor substrate 11; accordingly, the area of the pixel Px is enlarged and the number of pixels which can be formed in a predetermined size is reduced.
When the area of the bias semiconductor region 57 is reduced for minimizing the enlargement of the area of the pixel Px, a bias potential cannot be stably impressed on the semiconductor substrate 11, and noise resistance is degraded.
Accordingly, the present invention aims at realizing a reduction in the area of a pixel without degrading noise resistance.